Dual-reflector microwave antennas are known which minimize signal blockage at the main reflector dish aperture by utilizing small-diameter feed horns and subreflectors. These small-diameter feed horn and subreflector combinations produce a good radiation pattern envelope (RPE) in the near-in side lobes between 3.degree. and 10.degree. from the antenna axis. Unfortunately, the small-diameter feed horn characteristically displays a wide angle beam which causes an illumination pattern at the surface of the subreflector which is larger in area than the subreflector surface area. Consequently, some portion of the microwave energy fed from the small diameter feed horn spills past the periphery of the subreflector surface. The effect of energy spillover is a degradation in antenna performance in the side lobe region between 3.degree. and 180.degree. from the antenna axis.